The present invention relates to a flow divider valve assembly, and more particularly, to one in which the modulating piston is of the center-flow type.
There are many known valve assemblies which are utilized to divide a flow of fluid between a priority flow utilization device, such as a power steering system, and an excess flow utilization device, such as the hydraulic motor of an auxiliary mechanism associated with a vehicle. One of these known flow divider valve assemblies includes a piston or valve spool having an axially extending internal chamber which is connected with an inlet passage by an orifice or aperture in the wall of the valve spool. The central chamber is open at one end of the valve spool to enable fluid to flow from the chamber to a priority flow outlet passage.
During operation of the power steering system, the open end of the chamber is unrestricted so that fluid can flow freely from the chamber to a priority flow outlet. At this time, the rate of fluid flow is determined by only the size of the orifice in the wall of the valve spool. When the auxiliary mechanism is active, the valve spool is shifted to move the open end of the chamber in the valve spool into a telescopic relationship with a projection on a modulating plug and the resulting orifice defined by the end of the spool and the projection on the plug modulates or restricts flow to the priority flow outlet.
Although flow divider valves constructed as described above have been generally satisfactory in operation, the production costs have been relatively high as a result of the extremely small clearance required between the external surface of the projection on the modulating plug and the internal surface of the valve spool. In addition, the use of the telescoping modulated plug has made it impractical to reduce the control flow to the priority port (i.e., the low flow rate when the priority device is not in operation), to a desirably low level, because of the fear of the modulating plug jamming within the valve spool, which would prevent subsequent flow to the priority device, even upon demand.
This inability to further reduce the controlled flow necessitated a larger pump output than was actually utilized, with the remainder being wasted. For example, if the priority flow to the steering system were 25 gpm and the controlled flow could be reduced only to about 7 gpm, and assuming further a requirement by the auxiliary mechanism of about 28 gpm, it may be seen that the pump must be capable of an output of at least 35 gpm (28 + 7) even though neither the steering nor auxiliary mechanism ever requires more than 28 gpm (this type of valve is used in a system in which the priority device and the auxiliary mechanism never simultaneously require a full flow). Therefore, about 20% of the pump output represents wasted pump capacity and energy, necessitated by the inability of prior art flow dividers to minimize or eliminate the controlled flow to the priority device during operation of the auxiliary mechanism.